Electron tube radio frequency generator



y 29, 1951 D. H. PREIST 2,554,500

ELECTRON TUBE RADIO FREQUENCY GENERATOR Filed Aug. 3, 1948 5 Sheets-Sheet 1 POWER OUTPUT T0 LOAD 8+ 2 3 44- 30 so 8 i7 '5 413 30 .3! 31 oar/ 07 RESONATOR l7 l4 /7 2 2 2 3 l8 46 I8 24 24 INPUT 21 REM/M70}? 55 33 as 3a POWER INPUT FROM DEIVE I i INVENTOR. 5 Donald h. Preis? ATTORNEY y 29, 1951 D. H. PREIST 2,554,500

ELECTRON TUBE RADIO FREQUENCY GENERATOR Filed Aug. 3, 1948 5 Sheets-Sheet 2 INVENTOR. Dona/a h. Pre/s? symfi f ATTORNEY May 29, 1951 D. H. PREIST Filed Aug. 3, 1948 POM/ER OUTPUT TO LOAD 3/ 3/ our ur RESON/ITaR g 2 /4 I k 3 g 18 g 31/ w T Z 15 2 1 a 47 mPuT was-OM70? /Z 24 I t 25 -/9 wj 4 v ELIZ. g. 3

IN VEN TOR.

Donald H. Pre/s? BY M54 ATTORNE Y D. H. PREIST ELECTRON TUBE RADIO FREQUENCY GENERATOR May 29, 1951 Filed Aug. 3, 1948 5 Sheets-Sheet 4 INVENTOR. Donald H. Pre is?" ATTORNEY y 29, 1951 D. H. PREIST ELECTRON TUBE RADIO FREQUENCY GENERATOR Filed Aug. 3, 1948 5 Sheets-Sheet 5 POWER OUTPUT 7'0 LOAD OUTPUT RE SONA 70/1 IN VEN TOR. Dona/o H. Pre/sf BY flag/5J ATTORNEY Patented May 29, 1951 UNITED STATES PATENT OFFICE ELECTRON TUBE RADIO FREQUENCY GENERATOR Application August 3, 1948, Serial No. 42,171

15 Claims. 1

My invention relates to generators of radiofrequency power using electron tubes, and more particularly to high-power generators using conventional type negative gl'id tubes.

The broad object of my invention is to provide an R. F. generator capable of delivering large orders of power, in the higher frequency ranges, say above 100 mes/sec.

Experience in the past has indicated that in order to increase the power output of R. F. generators, whether amplifiers or oscillators, it is necessary either to make larger tubes or use several tubes together. The first approach of increasing the physical size of a single tube is undesirable for many reasons. One is that increased size is incompatible with good electrical performance, particularly at the higher frequencies. Another is that the tube production problems increase with the tube size, after a certain point, and this also becomes a serious economical factor to the user because of the large loss sustained when a high-cost tube fails. The second approach of using smaller tubes has decided advantages from the standpoint of optimum tube design and ease of tube manufacture, but R. F. generating systems heretofore employed using a plurality of tube units have not been satisfactory, and for some applications are wholly inoperable. For example, conventional circuits connecting a plurality of tube units in parallel are limited as regards the number of tube units that can be successfully employed at the higher frequencies, because of decreasing efliciency with increasing number of units, due to parasitic or undesired oscillations or to losses accountable by asymmetry of circuit connections. This decrease in efficiency, for a given number of tube units, becomes increasingly worse compared to a single unit as the operating frequency is raised. The power output falls off accordingly, and it is not possible in conventional circuits to obtain from n number of tube units a power output i equal to n times that of a single unit.

I In view of these limitations another object of imy invention is to provide an R. F. generator! .1 J

embodying a plurality of tube units wherein the; power output obtainable at the higher frequencies is n times that of a single tube unit, other words, if say five tube units are employed? the power output is substantially five times that of a single unit. E Still another object is to provide such a mul-i tiple unit tubegenerator which may be designed; to operate either as an amplifier or as an oscil lator.

i I I to 2 The invention possesses other objects and fea tures 'of advantage, some of which, with the foregoing, will be set forth in the following description of my invention. It is to be understood that I do not limit myself to this disclosure of species of my invention as I may adopt variant embodiments thereof within the scope of the claims.

Referring to the drawings: Figure 1 is a vertical sectional view taken along the axis of an amplifier version of the generator embodying my invention; and

Figure 2 is a transverse sectional view of .the

same taken along a plane indicated by line 2-2 of Figure 1.

Figure 3 is a view similar to Figure 1 showing an oscillator version of my generator; and

Figure 4 is a sectional viewgof the same taken along a plane indicated by line 44 of Figure 3.

Figure 5 is a view similar to Figure 3 showing a modified form of oscillator; and

Figure 6 is a sectional view of the same taken along a plane indicated by line 6-6 of Figure 5.

In terms of broad inclusion, the radio-frequency generator of my invention'comprises a plurality of electron tube units disposed in a 'circle'about an axis and each having electrodes,

and an annular cavity resonator common to the tube units arranged coaxially with the circle and having an annular conductor connected to an electrode of each of the tube units. This symmetrical arrangement of a cavity resonator with respect to a plurality of electron tube units is an important feature of the invention. Such an annular resonator may be used for either the output or input resonant circuits of the tube units, or for both. In my preferred generator an annular output resonator is provided having an inner annular conductor connected to an anode of each of the tube units, and a similar annular input resonator is provided coaxial with the output resonator and having an inner annular conductor connected to a cathode of each of the tube units, adjustable means being arranged in the resonators for tuning them to the operating frequency.

Continuing the broad statement, my R. F. generatof may be designed for operation either as an amplifier or as an oscillator. Designed as an amplifier the generator has a transverse wall conductor connected to outer wall conductors of the resonators and also connected to a grid of each of the tube units. Power output from the amplifier is preferably fed by an axially extending hollow transmission line coupled to the output resonator, and power input to the amplifier is preferably fed by a similar transmission line coupled to the input resonator. The coupling is preferably accomplished by means of circular slots communicating between the transmission lines and the respective resonators to maintain the symmetry of the generator. Designed as a selfexcited oscillator the input resonator of my RF. generator functions as the excitation circuit, and feedback means are provided for feeding energy from the output resonator to the input resonator. This feedback means preferably comprises a separate transverse conductor connected to the grids of the tube units and spaced from the transverse wall conductor so that these parts function as condenser members for capacitatively coupling the resonators to establish the desired feedback of energy from the output resonator to the input resonator.

In greater detail and referring first to Figures 1 and 2 of the drawings, the amplifier version of my improved R. F. generator comprises a plurality of electron tube units I disposed in a circle about a common axis, which tube units are of like construction and have like characteristics While five tube units are shown, it is understood that any desired number may be employed depending upon the power output required, an odd number of tube units being preferred. Any conventional type of negative grid electron tube may be used for the units I, the triode type of tube illustrated having a cathode 2, grid 3 and anode 4, the anode being external and all the electrodes being preferably cylindrical and coaxial. The tube units employed also preferably have coaxial terminals for the electrodes, such as the cathode terminal 6 opposite the anode and the grid terminal ring I interposed in the glass envelope wall between .the cathode terminal and anode. The heating structure for the cathode is not shown but may comprise any suitable means such as an inner filament for heating the cathode cylinder 2 by electron bombardment, in which case the filament leads preferably extend out through the tubularcathode terminal 6. A tube of this general type is disclosed in the copending application of William W. Eitel et al., Serial No. 11,916, filed February 28, 1948.

My improved R. F. generator has an annular cavity resonator common to the tube units and provides a resonant circuit for such units, which resonator is arranged coaxially with the circle of the tube units and has an inner annular conductor connected to an electrode of each of the tube units. This symmetrical arrangement of the cavity resonator with respect to a plurality of tube units is an important feature of the invention. In the amplifier type of generator illustrated in Figure 1, both the output and input resonant circuits are made up of such annular resonators. These resonators have annular vU.-shaped cavities defined by metallic boundary walls, namely, the output resonator 8 forming the cavity 9 and the input resonator II forming the cavity I2.

It will thus be noted that in the preferred embodiment shown in the drawing, each resonator comprises two cavity sections, each section being constituted by the space between a pair of concentric cylinders. The length of each section, measured axially of the circle of tube units, is

substantially greater than the width of the sec- .tion, measured radially of the circle of tube units, .i. e. the difference in radius of the concentric .cylinders which define the section (ignoring the thickness of the cylinders). An annulus having a greater axial than radial dimension, measured as described, is defined hereinafter as an axially extending annulus.

Output resonator 8 comprises a pair of cylindrical wall conductors I3 and I4 and an inner annular conductor I6 interposed between the wall conductors, the inner conductor being shorter than the wall conductors. The inner conductor I5 is preferably of hollow construction with cylindrical sides I'I joined by a bottom ring I8. Input resonator I I is preferably similar to and coaxially aligned end-to-end with the input resonator. It comprises a pair of cylindrical wall conductors I9 and 2I and an inner annular conductor 22 having cylindrical sides 23 joined by a top ring 24. With the end-to-end arrangement of the resonators illustrated the outermost wall conductors I3 and 2I are abutted, or constructed as single shell, and the tube units I are interposed between the resonaters.

Inner conductor I6 of the output resonator is connected to the anode 4 of each of the tube units, this connection being preferably made to the bottom ring I8 which is apertured so that the external anodes 4 project up into the hollow inner conductor. In a similar manner inner conductor 22 of the input resonator is connected to the cathode 2 of each of the tube units, connection being made to the cathode terminals 6 which pref erably project downwardly through apertures in the top ring 24 of the hollow conductor. The grids 3 of the several tube units are connected together and to the outermost wall conductors I3 and 2I of the resonators by a transverse wall conductor 26. In the particular structure illustrated this transverse conductor also forms a common end wall of the two resonators. Tube units I project through the wall 26 which is apertured for that purpose and connection is made directly to the grid terminal rings I on the tube envelopes. Suitable leads for the cathode heater means of the several tube units may extend out through the hollow conductor 22, and any suitable cooling system (also not shown) may be connected to the anodes 4 through the hollow conductor I6.

Inner conductors I6 and 22 of the two cavity resonators are mechanically held in position by annular supports 2'! and 28 of suitable insulating material fastened to the upper and lower ends of conductors I3 and 2I respectively. Any suitable material such as brass may be used for the conductors.

Adjustable means are provided for tuning the output and input resonators to the desired operating frequency. For this purpose a pair of annular metal plates 29 are provided in the output resonator, on the opposite sides of conductor I6, so as to form the upper end wall of cavity 9. These plates are slidably mounted on the inner conductor I6, and axial adjustment is achieved by means of plunger rods 30 of insulating material connected to the plates and projecting out through support 21. The rods 3I may be connected externally to insure that the plates 29 are adjusted in unison. Plates 29 are connected to the inner conductor only and have cylindrical flanges 3I closely spaced to the wall conductors I3 and It so that the device also functions as e choke to confine the R. F. and isolate the D. anode voltage. For this purpose the flanges 3| of the choke are made effectively a quarter wave long at the operating frequency, a telescopinsleeve (not shown) being preferably provided on the flange to adjust its length. The positive similar to that described for the amplifier.

M A-J MHiUR 6 anode potential may thus be applied by connection directly with the inner conductor l6 as indicated at 32. This anode voltage may either be continuous or in the form of pulses, depending upon the operation desired. Tuning the output resonator is accomplished by adjusting the end plates 29 to make the cavity 9 the desired length for a selected operating frequency, as will be readily understood.

In a like manner a pair of annular plates 32 are provided in the input resonator ll, slidable on the inner conductor 22, and having flanges 33 spaced from the wall conductors I9 and 2| to function as a choke to confine the R. F. and isolate the D. C. voltages. Adjustment of end plates 32 is accomplished by rods 34 to tune the input resonator to the desired operating frequency, in a manner similar to that described for the input resonators. Bias voltage for the grid is applied by connection made to the transverse wall member 26 as indicated at 36.

Radio-frequency input driving power to the amplifier is preferably transferred to the input resonator H from a suitable source of drive by xiieans of a hollow transmission line 31, preferably of the coaxial type having an inner conductor 38 and an outer conductor 39. This transmission line extends axially of the resonator with the inner conductor 38 terminating at the transverse wall conductor 26 and the outer conductor 39 formed as a continuation of the innermost wall conductor 19 of the resonator. Such arrangement is, of course, made possible by the annular shape of the resonator. Energy coupling means between the transmission line and input resonator preferably comprises a circular slot 4| formed by spacing the upper end of conductor Hi from the transverse wall 26. The circular arrangement of this coupling slot is desirable because it provides uniform coupling of energy from the transmission line to the annular cavity I2, which is another feature made possible by the symmetrical arrangement of my improved generator construction.

Radio-frequency output power from the amplifier is preferably transferred from the output resonator 8 to a suitable load by means of a hollow transmission line 42. This transmission line also extends axially of the resonator and is preferably similar to that described for the input, namely, a coaxial type of line having an inner conductor43 terminating at the transverse wall 26 and having an outer conductor 44 formed as part of the innermost wall conductor l4 of the output resonator. A circular slot 46 serves to couple energy from the output resonator to the transmission line 42.

Other suitable means may be employed for transferring and coupling power into and out of the resonators, but the coaxial and symmetrical arrangement shown is preferred because it is capable of efiiciently handling large, orders of power.

Figures 3 and 4 show an oscillator version of my generator. The input and output resonators 8 and II are preferably of annular construction The tube units I are disposed in a circle located between the resonators with the anodes 4 and cathll serves as the input or excitation circuit. Transverse wall conductor 26 is not connected directly to the grids but has apertures 41 providing clearance holes for the tube units. Innermost wall conductor l9 of the input resonator terminates at the transverse wall 26, and the adjustable end plates 32 are simply shorting bars slidable between the inner conductor and the wall conductors.

Means are provided for establishing feedback of energy from the output resonator to the input resonator to sustain oscillation. The feedback system employed preferably comprises condenser members for capacitatively coupling the resonators. As illustrated, an annular metallic condenser member 48 is connected to the grid 3 of each of the tube units and is spaced from a second condenser member connected to the outermost wall conductors of the resonators. which second condenser member is formed by the transverse wall conductor 26 in the oscillator configuration shown. Condenser member 48 also preferably extends transversely of the resonator axis and preferably comprises a fiat ring-shaped plate lying parallel with the condenser member 26. Plate 48 is preferably supported wholly by the tube units I by direct connection to the grid terminal rings I thereof, which connection is preferably slidable to adjust the spacing between the condenser plates.

By this arrangement an electrostatic coupling is provided between the two resonators, whereby feedback of energy is provided from the output resonator 8 to the input resonator II in the proper phase to sustain oscillation. In the final adjustment the feedback or excitation voltage may be varied b adjusting the spacing of the condenser members 48 and 26 and adjusting the position of the shorting bars 32. An important feature of this feedback system, including the annular condenser member 48 connected to the grids of all the tube units and coaxial with the circle of units, is that the symmetrical arrangement of the feedback system with respect to the tube units and annular resonators provides for an efiicient feedback of energy which is capable of handling relatively large orders of power.

Bias voltage is supplied from an outside connection 49 to the grids through a wire 5| connected to member 48 and entering the resonator through a suitable R. F. choke 52.

Figures 5 and 6 show a modified type of oscillator construction employing individual input resonators 53 for each of the tube units rather than the common annular input resonator above described. In this case the input resonators each comprise an outer tubular conductor 54 terminating at the transverse wall conductor 26 and an inner tubular conductor 56 connected to the cathode terminal 6. An end plate 51 slid able on the inner conductor and flanged to provide an R. F. choke is provided in each resonator, and is adjustable by rods 56 projecting out through the insulating supporting disk 49 for tuning purposes. Feedback coupling from the common annular output resonator to the plurality of input resonators is by the electrostatic means previously described, involving a single annular condenser member 48 connected to the grids of the tube units. This modified type of oscillator structure, involving separate input resonators, preferred in cases where it is desired to individually tune the input circuits of the tube units. In other respects the oscillator structure is the same as that first described,

and has all the advantages of the symmetrical arrangement of the tube units with respect to the common output circuit. a

In my improved R. F. generator, either as an amplifier or as an oscillator, the overall diameter of the generator may be increased indefinitely to accommodate an indefinite number of tube units. The power output capability is thus limited largely by the space available. Furthermore, the multiple unit tube generator will operate Well in the higher frequency ranges, say above 500 mc./sec., without loss of efficiency compared to that of a single tube unit.

Operation As an amplifier:

In the multiple unit tube annular generator illustrated in Figure 1 the symmetrical arrange ment of the annular resonators B and H with respect to the tubes is to be noted because this structural configuration promotes the formation of symmetrical R. F. fields in the cavities of the resonators. The driving power which is fed through transmission line 31 induces an axially symmetrical R. F. field in cavity l2 of the input resonator II. This occurs by virtue of the circular slot 4| which effectively puts the input transmission line in series with .the annular input cavity I2. Such symmetrical R. F. field in the input resonator applies equal R. F. voltages in the same phase between the grids and cathodes of all the tube units. With suitable external potentials applied to the tube electrodes, these equal grid-to-cathode voltages produce equal variations in the anode currents which also are in phase. Since the annular output resonator 8 is symmetrically connected to the tube units, and since the load is symmetrically coupled to the output cavity 9 by the circular slot' 46, equal R. F. impedances are presented by the loaded annular output cavity to all the tube units. An axially symmetrical R. F. field is thus produced in the output resonator, of greater intensity than that in the input resonator corresponding to the amplification of the tube units. This power amplification is obtained in my multiple unit tube generator without loss of efiiciency as the frequency is raised up to the limiting frequency of the tube units themselves. The total power output, as measured at the load, is substantially times that obtainable from a single tube unit in an efficient single unit tube generator.

As an oscillator:

Referring to Figure 3, the symmetrical arrangement of the annular resonators with respect to the tube units in the self-excited oscillator version of the generator also promotes the formation of symmetrical R. F. fields in the cavities of the resonators. It will be noted that the feedback system, which capacitatively couples the resonators, involves a condenser member 48 which is also symmetrical and coaxial with oscillator structure. The feedback energy thus induces or excites an axially symmetrical R. F. field in cavity l2 of the input resonator H. In other respects the generator operates similarly to the amplifier version above described, it being noted that the output coupling or loading system for the output resonator is identical with that described for the amplifier. The modified oscillator in Figure 5, having individually tunable input resonators of several tubes, has the advantage of being able to compensate for the variable efiects due to small differences that 8 may exist in characteristics between the tubes. Otherwise the generator operates in a manner similar to that described in connection with Figure 3.

While I have described my generator in connection with triode units, it is understood that tube units having additional electrodes such as tetrodes may be employed, in which case additional annular, coaxial and symmetrical circuit members are used to make connection to the extra electrodes.

' I claim:

1. A radio-frequency generator comprising a plurality of electron tube units disposed in a circle about an axis and each having electrodes, a resonator comprising a pair of axially extending concentric annular cavity sections, the axial dimension of each of said cavity sections being substantially greater than the radial dimension thereof, the axis of the annulus defined by said cavity being coincident with said first named axis,

said cavity having a conductor electrically connected to an electrode of each of said tube units, and tuning means in the resonator for adjusting the axial length of said cavity sections.

2. A radio-frequency generator comprising a plurality of electron tube units disposed in a circle about an axis and each having electrodes including an anode and cathode and grid, an output resonator comprising a pair of axially extending concentric annular cavity sections, the axial dimension of each of said cavity sections being substantially greater than the radial dimension thereof, the axis of the annulus defined by said cavity being coincident with said first named axis, said cavity having a conductor electrically connected to the anode of each of said tube units, an input resonator comprising a pair of concentric annular cavity sections, the axis of the annulus defined by said cavity being coincident with said first named axis, said cavity having a con- .ductor electrically connected to the cathode of each of said tube units, a conductor common to said resonators and electrically connected to the .grid of each of said tube units, and tuning means 'in the resonators for adjusting the axial length of said cavity sections.

3. A radio-frequency generator comprising a plurality of electron tube units disposed in a circle about an axis and each having electrodes, a resonator comprising an annular cavity, the axis of the annulus defined by said cavity being coincident with said first named axis, said cavity having a conductor electrically connected to an electrode of each of said tube units, a hollow transmission line extending axially of said circle, and

energy coupling means comprising a circular slot communicating between said line and resonator.

4. A radio-frequency generator comprising a plurality of electron tube units disposed in a circle about an axis and each having electrodes including an anode and cathode, an output resonator comprising an annular cavity, the axis of the annulus defined by said cavity being coincident with said first named axis, said cavity having a conductor electrically connected to the anode of each of said tube units, an input resonator comprising an annular cavity, the axis of the annulus onator, a hollow output transmission line extend-. ing axially of said circle, and energy coupling means comprising a circular slot communicating between said output line and output resonator.

5. A radio-frequency generator comprising a plurality of electron tube units disposed in a circle about an axis and each having electrodes including an anode and cathode and grid, an output resonator comprising an annular cavity, the axis of the annulus defined by said cavity being coincident with said first named axis, said cavity having a cylindrical conductor electrically connected to the anode of each of said tube units, an input resonator comprising an annular cavity, the axis of the annulus defined by said cavity being coincident with said first named axis, said cavity having a cylindrical conductor electrically connected to the cathode of each of said tube units,

and a conductor common to said resonators comprising a member extending transversely of said axis and electrically connected to the grid of each of said tube units.

6. A radio-frequency generator comprising a plurality of electron tube units disposed in a circle. about an axis and each having electrodes including an anode and cathode and grid, an output resonator comprising an annular cavity, the axis of the annulus defined by said cavity being coincident with said first named axis, said cavity having a cylindrical conductor electrically connected to the anode of each of said tube units, an

input resonator comprising an annular cavity, the axis of the annulus defined by said cavity being coincident with said first named axis, said cavity having a cylindrical conductor electrically connected to the cathode of each of said tube units, a conductor common to said resonators comprising a member extending transversely of said axis and electrically connected to the grid of each of said tube units, a hollow transmission line extending axially of said circle, and energy coupling means comprising a circular slot adjacent said transverse member and communicating between said line and one of the resonators.

7. A radio-frequency generator comprising a plurality of electron tube units disposed in a circle about an axis and each having electrodes including an anode and cathode and grid, an output resonator comprising an annular cavity, the axis of the annulus defined by said cavity being coincident with said first named axis, said cavity having a cylindrical conductor electrically connected to the anode of each of said tube units, an input resonator comprising an annular cavity, the axis of the annulus defined by said cavity being coincident with said first named axis, said cavity having a cylindrical conductor electrically connected to the cathode of each of said tube units. a conductor common to said resonators comprising a member extending transversely of said axis and electrically connected to the grid of each of said tube units, a hollow input transmission line extending axially of said circle, en-

'ergy coupling means comprising a circular slot adjacent said transverse member and communicating between said input line and input resonator, a hollow output transmission line extending axially of said circle, and energy coupling means comprising a circular slot adjacent said transverse member and communicating between said output line and output resonator.

8. A radio-frequency generator comprising a plurality of electron tube units disposed in a circle about an axis and each having electrodes including an anode, an annular output cavity resonator common to the tube units arranged coaxially with said circle and having an annular conductor connected to the anode of each of said tube units, said resonator comprising an axially extending annular cavity, the axial dimension of said cavity being substantially greater than the radial dimension thereof, tuning means in the resonator for adjusting the axial length of said cavity, and input resonator means having conductor means connected to other electrodes of said tube units, and coupling means establishing feedback of energy from the output resonator to the input resonator means.

9. A radio-frequency generator comprising a plurality of electron tube units disposed in a circle about an axis and each having electrodes including an anode and grid and cathode, an annular output cavity resonator common to the tube units arranged coaxially with said circle and having an annular conductor connected to the anode of each of said tube units, said resonator comprising an axially extending annular cavity, the axial dimension of said cavity being substantially greater than the radial dimension thereof, tuning means in the resonator for adjusting the axial length of said cavity, and input resonator means having conductor means connected to the cathodes of the tube units, and capacity coupling means establishing feedback of energy from the output resonator to the input resonator means, said coupling means including a condenser member connected to the grid of each of the tube units.

10. A radio-frequency generator comprising a plurality of electron tube units disposed in a circle about an axis and each having electrodes including an anode and grid and cathode, an annular output cavity resonator common to the tube units arranged coaxially with said circle and having an annular conductor connected to the anode of each of said tube units, said resonator comprising an axially extending annular cavity, the axial dimension of said cavity being substantially greater than the radial dimension thereof, tuning means in the resonator for adjusting the axial length of said cavity, and input resonator means having conductor means connected to the cathodes of the tube units, and capacity coupling means establishing feedback of energy from the output resonator to the input resonator means, said coupling means including a plate-like condenser member extending transversely of said axis and connected to the grid of each of the tube units.

11. A radio-frequency generator comprising a plurality of electron tube units disposed in a circle about an axis and each having an anode and grid and cathode, an annular output cavity resonator common to the tube units and arranged coaxially with said circle, the output resonator having a pair of cylindrical wall conductors and an inner annular conductor therebetween, said inner con ductor of the output resonator being connected to the anode of each of the tube units, an annular input cavity resonator common to the tube units and arranged coaxially with said circle, the input resonator having a pair of cylindrical wall conductors and an inner annular conductor therebetween, said inner conductor of the input resonator being connected to the cathode of each of said tube units, the axial dimension of each of said resonators being substantially greater than the radial dimension thereof, tuning means in said resonators for adjusting the axial length thereof, and means including a pair of condenser members for capacitatively coupling the reso- "12. A radio-frequency generator comprising a lurality of electron tube units disposed in a circle about an axis and each having an anode and grid and cathode, an annular output cavity resonator common to'the tube units and arranged coaxially with said circle, the output resonator having a pair of cylindrical wall conductors and an inner annular conductor therebetween, said inner conductor of the output resonator being connected to the anode of each of the tube units, an annular input cavity resonator common to the tube units and arranged coaxially with said circle, the input resonator having a pair of cylindrical wall conductors and an inner annular conductor therebetween, said inner conductor of the input resonator being connected to the cathode of. each of said tube units, the axial dimension of each of said resonators being substantially greater than the radialpdimension thereof, tuning means in said resonators for. adjusting the axial length thereof, a transverse conductive member connected to the outermost ,walls of the resonators, and a transversely extending conductive member connected to the grid of each of the tube units and spaced from said first conductive member for capacitatively coupling the resonators to establish feedback of energy from the output resonator to the input resonator.

13. A radio-frequency generator comprising a plurality of electron tube units disposed in a circle about an axis and each having electrodes including an anode and cathode and'grid, an output resonator comprising a pair of concentric annular cavity sections defined by four concentric cylinders, certain of said cylinders defining a conductor electrically'connected to the anode of each of said tube units, an input resonator comprising a pair of concentric. annular cavity sections defined by four concentric cylinders, certain of said last-named cylinders defining a conductor electrically connected to the cathode of each of said tube urrfts, a conductor common to said resonators and electrically connected to the grid of each of 12 said tube units, and tuning means in the resonators for adjusting the axial length of said cavity sections.

14. A radio-frequency generator comprising a plurality of electron tube units disposed in a circle about an axis and each having a plurality of electrodes, an output resonator comprising a pair of concentric annular cavity sections defined by four concentric cylinders, certain of said cylinders defining a conductor electrically connected to an electrode of each of said tube units, an input resonator comprising a pair of concentric annular cavity sections defined by four concentric cylinders, certain of said last-named cylinders defining a conductor electrically connected to a second electrode of each of said tube units, a conductor common to said resonators and electrically connected to a third electrode of each of said tube units, and tuning means in the resonators for adjusting the axial length of said cavity sections.

15. A radio-frequency generator comprising a plurality of electron tube units disposed in a circle about an axis and each having electrodes including an anode, an annular output cavity resonator common to the tube units arranged coaxially with said circle and having a conductor electrically connected to the anode of each of said tube units, said resonator comprising an axially extending annular cavity, the axial dimension of said cavity being substantially greater than the radial dimension thereof, tuning means in the resonator for adjusting the axial length of said cavity, and input resonator means having conductor means electrically connected to another electrode of each of said tube units.

DONALD H. PREIST.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,239,421 Haeff Apr. 22, 1941 2,241,119 Dallenbach May 6, 1941 2,284,405 McArthur May 26, 1942 2,353,742 McArthur July 18, 1944 2,381,320 Tawney Aug. '7, 1945 

